Magnetic trip latching system for circuit breakers



March 11, 1969 G. w. KNECHT 3,432,731

MAGNETIC TRIP LATCHING' SYSTEM FOR CIRCUIT BREAKERS Filed Dec. 14, 1966 United States Patent Oflice 3,432,781 Patented Mar. 11, 1969 MAGNETIC TRIP LATCHING SYSTEM FOR CIRCUIT BREAKERS George W. Knecht, Brooklyn, N.Y., assignor to Murray Manufacturing Corporation Filed Dec. 14, 1966, Ser. No. 601,580 US. Cl. 335-172 Claims Int. Cl. Htllh 9/20 ABSTRACT OF THE DISCLOSURE This invention relates to magnetic trip devices generally, such as used in electromagnetic circuit breakers, and in particular, to a novel latching system particularly applicable to alternating current, and where only a low magnetic tripping force is available.

Existing alternating current type magnetic trip devices have become distinct from the direct current type, utilizing the AC. cycle to induce an oscillating movement which magnifies unlatching forces by momentum and impact. In general, the trip armature is spring biased as a separate member which has the function of oscillating and impacting the latching member from its latched position. The latching member is itself spring biased and comprises a second section which functions via a linkage to maintain the circuit contacts in closed position. Both the latch and trip armature anguarly displace to effect their functional objectives.

Unfortunately, existing devices are not sufficiently positive in AC. operation to be completely satisfactory. Further, an increased latching force necessitates an in crease in the trip force which is provided by the magnetic circuit. Hence, the magnetic circuit must be designed to handle a range of latching forces within the tolerances assigned to the various members. Since the upper limit of forces may be rather large, the magnetic circuit must be commensurately large.

Accordingly, it is the object of this invention to obviate the foregoing disadvantages of conventional alternating current magnetic trip devices, is economical Briefly, the invention is predicated upon the concept of an integral system having a latching bias moment; a trip armature balance force which supports oscillation; and a novel arrangement of pivot and force balances which allows it to latch and unlatch varying latch forces with a minimum magnetic field. This is accomplished by an inverse dependency between the latching force and the trip armature bias force. In other words, when less bias is necessary because of a larger latching force, the system automatically compensates by effecting this result.

The above mentioned and other features and objects of this invention and the manner of attaining them will become more apparent and the invention itself will best be understood by reference to the following description of an embodiment of the invention taken in conjunction with the accompanying drawings wherein:

FIG. 1 is an exploded perspective illustration of the frame and trip armature assembly.

FIG. 2 is a plan view of the electromagnetic circuit and latching lever.

FIG. 3 is a detail of the frame-trip armature rocking junction as well as the latch lever-trip armature point of contact.

FIGS. 4 and 4a are forced diagrams used in explaining the invention.

FIGS. 5 and 6 illustrate the invention arrangement during the application of operational magnetic forces.

Turning now to the invention, and in particular, to FIG. 1, the component configuration may be seen in an exploded perspective. This figure also illustrates the ease with which the invention arrangement may be manufactured and assembled. The trip armature 10 comprises parts 11 and 12; the former being of rigid material, and the latter of leaf spring material. The trip armature is rockably assembled onto the frame or yoke 20 by the placing of the rectangular opening 13 in the leaf spring 12 over the neck of frame 20 to eventually rest on the shoulders 20'. The T-shaped opening 14 in the trip armature component 11 is then placed over the neck of the frame 20, the armature portion 11 then being slid forward under leaf spring pressure so that the neck of the frame moves into the smaller width portion of the T-shaped opening. The rest position is one where the flanges 20" of the frame retain the trip armature as an integral member. Latching knub 16 on trip armature member 11 is snapped into the second rectangular opening 17 in the leaf spring member 12.

In practice, the operational arrangement is that shown in FIG. 2. The electro-magnetic circuit comprises a coil 40, which is generally connected in series (not shown) with the circuit it is designed to protect, within which is disposed core 41. The core carries a frame or yoke 20 upon which trip armature 10 is rockably mounted as was previously described. Two air gaps A and A complete the magnetic loop. Latch lever 30 is biased in direction of the arrow 31, by any well known means (such as a spring) and it is this member which generally fulfills the functional requisite, via a linkage arrangement, of holding and releasing the circuit contacts. A fulcrum 22 which is preferably formed from the molded housing embracing the magnetic device of the invention performs a function which will be explained with reference to FIG. 3. It may be noted that this fulcrum may also be made as an integral part of the frame.

FIG. 3 is a detail of the dynamic portion of the device depicted in FIG. 2. From this figure it may be seen that offset points a and b provide the trip armature biasing angular moment c; point b acting upon the leaf spring to deflect it, and point a restraining the upward motion of the trip armature and effecting the biasing moment.

FIGS. 4 and 4a show the produced balancing of forces. The latch force which exists by virtue of the biasing on the latching lever acts at point e of the latching knub 16 of the trip armature and is transmitted through the angle 0 to point a of the outer edge of the rectangular opening 17 in the leaf spring. This latter force acts in this manner because of the pressure exerted by the latching lever tending to move the trip armature to the left and the restraining of such movement by the leaf spring at point g of the outer edge of rectangular opening .13 (via the frame portion 20 resting against wall 22). The result is moment 1 which is opposite to biasing moment 0 (FIG. 3).

This opposite moment puts the system in force balance. Since the latching force varies with different devices due to component tolerances during manufacture, the arrangement described automatically compensates. That is, when the latching force increases, the trip armature bias force decreases, and vice vera, thereby allowing the same magnetic field to be effective. In other words, when a smaller bias is necessary because of a larger latching force, the system automatically compensates and effects this result.

With this force balance, the relationship between the trip armature knub and latching lever is such that during low latching forces, the trip armature maintains a high bias moment, and during high latching forces, the trip armature maintains low or no biasing depending upon the magnitude of the latching force. At the extreme of high latching, force 3 will overcome moment c to the extent that the trip armature will move away from point a and no bias moment at all will exist.

The latching force ultimately transmits to pivot point g as previously mentioned, and this point is the major pivot point of the entire system.

FIG. illustrates the action of the system during the application of an oscillatory magnetic field (induced by an AC. current). The trip armature under the infiuence of magnetic forces at the air gaps A and A moves to deflect the leaf spring. Air gap A decreases partially while air gap A no longer exists. Following the alternating current peaks, the trip armature acts in response to leaf spring pressure to increase the air gap. It is to be noted that when the trip armature no longer contacts point a under the influence of magnetic peaks, the biasing moment 0 shown in FIG. 3 no longer exists.

This arrangementsupports an oscillatory motion with the trip armature pivoting about point j. Frictional force It between the knub point j and the latching lever is overcome by the rocking action at the contacting surfaces and the impact action when the trip armature closes the air gap and strikes the leaf spring solid to the flanges on the frame or yoke 20.

FIG. 6 shows the latching lever escaping the trip armature knub. As may be seen, neither air gap A nor A exists any longer, and both trip armature members have pivoted about point k with trip armature compression being effected between members 11 and 12.

When the device is unlatched, the contacts (not shown) open in any well known manner opening the circuit to the coil and eliminating the magnetic force. Upon a return of the latching lever during manual reset, the trip armature knub will re-latch by virtue of the biasing moment described in FIG. 3.

It bears mentioning that while the device has been described in particular with reference to AC. operation, the invention is also somewhat advantageous when applied to direct current devices. This arises as a result of the rocking action at the latch point and a signal impact which occurs when air gap A closes contributing to a reliable D.C. trip.

While the principles of the invention have been described in connection with specific apparatus, it is to be clearly understood that this description is made only by way of example and not as a limitation to the scope of the invention as set forth in the objects thereof and in the accompanying claims.

What is claimed is:

1. A magnetic trip latching device comprising an electromagnetic circuit including a coil; a magnetic core embraced by said coil; a frame member magnetically coupled to said core; a trip armature rockably mounted on said frame member; means including interacting portions of said frame and trip armature for effecting an angular bias moment on said trip armature; a latch lever disposed adjacent said frame member and biased away from the rockable mounting point between said trip armature said said frame member; and means co-acting between said trip armature and said latch lever and responsive to said latch lever bias for producing an external moment counter said angular bias moment, whereby the trip armature bias is dependent upon the biasing latch force value.

2. The magnetic trip latching device claimed in claim 1 in which said trip armature is supported on said frame member at a first bearing point, said angular bias moment means including a second bearing point on said trip armature offset from and biased apart from said first bearing point; said external moment acting to reduce the distance between said bearing points and hence said first angular moment.

3. The magnetic trip latching device claimed in claim 2 wherein said trip armature comprises a bent lever arm, and a leaf spring extending substantially between the ends thereof.

4. The magnetic trip latching device claimed in claim 3 wherein said lever arm and said leaf spring each have an aperture therein embracing a necked portion of said frame member, and wherein said interacting portions of said frame and trip armature include a portion of said leaf spring adjacent said aperture and a flange on said frame member contiguous said last mentioned portion.

5. The magnetic trip latching device claimed in claim 4 wherein said external counter moment producing means include knub on said lever arm passing through an aperture in said leaf spring, whereby said moment acts via the latch lever edge contiguous said knub and the leaf spring portion on the opposing side of said knub.

References Cited UNITED STATES PATENTS 8/1937 Arragg 335-274 5/1965 Ryckman 335-276 U.S. Cl. X.R. 

